An electrophotographic image forming apparatus is provided with an environmental sensor which detects temperature or humidity of the vicinity of a photoconductor surface. Image formation conditions such as a voltage applied to a charging roller are determined on the basis of information indicating an ambient temperature or an environmental humidity of a photoconductor, detected by the environmental sensor.
If an image forming apparatus includes a plurality of photoconductors, an environmental sensor is preferably provided in each of all of the photoconductors. However, it is desired to reduce the number of environmental sensors from the viewpoint of reducing cost. In this case, in the image forming apparatus, an ambient temperature of a photoconductor having the environmental sensor is used instead of an ambient temperature of a photoconductor not having the environmental sensor.
However, actually, there are many cases where there is a difference between an ambient temperature of a photoconductor having the environmental sensor and an ambient temperature of a photoconductor not having the environmental sensor. In this case, a charging state of a charging roller with respect to the photoconductor not having the environmental sensor is insufficient or excessive, and thus there is a probability that the quality of a formed image deteriorates.